A driver's torque demand may be split between an engine and an electric machine. The torque split between the electric machine and the engine may vary with operating conditions such as battery state of charge (SOC), driver torque demand, amount of hydrocarbon fuel stored in the vehicle, and other conditions. In addition, it may be desirable to operate an engine at its most fuel efficient operating conditions to reduce fuel consumption. However, if the driver demand torque is to be met and the engine is operated only at its most efficient operating conditions, operating efficiency of the electrical machine may be reduced more than is desired.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating a driveline, comprising: adjusting an engine to provide a torque, the torque being a portion of a driver demand torque; and adjusting an electric machine to provide an efficiency limited torque when a torque difference between the driver demand torque and the torque is in an efficiency dead-band of the electric machine.
By operating an electric machine to avoid operating conditions where efficiency of the electric machine may be reduced, the technical result of increasing operating efficiency of an electric machine may be achieved. For example, an engine operating in conjunction with the electric machine to propel a vehicle may be operated at efficient operating conditions to meet driver demand torque and improve engine efficiency. At the same time, the electric machine may be operated to avoid a dead-band operating range where electric machine efficiency may be less than is desired. In one example, the dead-band operating range may be at lower electric machine speeds and higher electric machine loads. Further, in some examples, operation of the engine may be adjusted to meet the driver demand torque during conditions where operation of the electric machine is being adjusted to avoid the dead-band operating range.
The present description may provide several advantages. For example, the approach may improve driveline efficiency. Further, the approach may conserve electrical energy for operating an electric machine to propel a vehicle. Additionally, the approach may be applied to hybrid vehicles that include gasoline, diesel, or gaseous fueled engines.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.